Objective:
– To show that sound waves require a medium for transmission.
Apparatus:
- Bell jar with speaker and microphone
- Power Supply AC/DC
- Vacuum plate
- Vacuum pump
- Audio generator (optional)
- Audio amplifier (optional)
- Speaker
- Leads
Method:
As the Bell jar is evacuated, the amplified sound dies away rapidly to nil.
If the air is then re-admitted slowly, the sound gradually returns, to its original level.
Note:
Use a frequency of about 700 Hz, due to transducer behaviour. Also, use fairly high gain setting on amplifier, and a low gain setting on signal generator.
Bell jar experiment – sound needs medium for propagation
– Video Created at the Rajesh Physics Center.